Perchloric acid

Toxicity to other aquatic organisms

Description of key information

Amphibians are identified as the most sensitive species to perchlorate. The effects on their development are considered as relevant for the derivation of the PNEC aquatic.

Additional information

One key study, an OECD report, is selected for toxicity to amphibians. This report summarizes the results from an OECD inter-laboratory study to assess the reliability of the amphibian metamorphosis assay for the detection of thyroid system-disrupting substances acting through different pathways. The Phase 1 validation study consisted in the optimisation of the protocol and exposure scenario. The Phase 2 of the validation study aimed at an inter-laboratory multi-chemical testing with an harmonised protocol. Three model substances representing different modes of action on the thyroid system were used in Phase-2 studies. These included sodium perchlorate. The perchlorate anion (PER) is a competitive inhibitor of thyroidal iodide uptake. A total of five non-GLP experiments with sodium perchlorate (Na-PER) as test substance were performed in five different laboratories (lab 1, lab 2, lab 3, lab 4 and lab 5).

Tadpoles (initiated at premetamorphic stage 51) of the South African clawed frog Xenopus laevis (20 tadpoles per replicate tank with 4 replicates per test concentration and control) were exposed during 21 days at four concentrations of the test substance (62.5, 125, 250 and 500 µg/L perchlorate anion) plus a dilution water control. Chemical treatment was accomplished by aqueous exposure of tadpoles in a flow-through system (flow rate 25 mL/min) and test chemicals concentrations were verified by analytical chemistry one a week. A battery of different apical morphological endpoints (developmental stage, hind limb length, whole body length, snout-vent length, wet weight) was analyzed after 7 and 21 days of exposure. Mortality was observed every day and histological analysis of thyroid gland tissue was performed with samples obtained after 21 days of exposure.

Analysis of growth-related parameters and mortality rates did not reveal signs of systemic toxicity for any of the tested perchlorate concentrations. Results from stage determination and hind limb length measurements showed perchlorate treatment to cause developmental delay in two experiments (lab 3 and lab 4) giving NOEC values ranging between 62.5 µg/L and 500 µg/L in nominal concentration.

Histological assessment of thyroid tissue was performed in four labs. Perchlorate treatment elicited marked effects on thyroid gland histology in all four studies. Incidence and severity of histological changes occurred in a concentration-dependent manner and provided strong evidence for disruption of the thyroid system by perchlorate, including depletion of colloid stores, glandular hypertrophy as well as hypertrophic and hyperplastic changes in the follicular epithelium. Consistent across laboratories, effects were observed already at the lowest tested concentration of 62.5μg/L perchlorate.

See the attached document in the section of PNEC derivation for discussion on this endpoint.